1. Field of the Invention
The present invention relates to a thin film transistor and manufacturing process thereof. More particularly, the present invention relates to a thin film transistor and manufacturing process thereof, the current leakage thereof is reduced while the thin film transistor is turned off.
2. Description of Related Art
In recent years, it has become more easy and fast for manufacturing thin film transistors with the advance in manufacturing technology of semiconductor. The appliance of thin film transistors is so widely in many fields such as chips for computer or mobile phones or thin film transistor liquid crystal display (TFT LCD) apparatuses. In TFT LCD apparatuses, the thin film transistors are served as the switches to discharge or charge the storage capacitors.
FIG. 1 is a cross-sectional view of a conventional thin film transistor. The conventional thin film transistor 100 is formed on a glass substrate 110. It comprises a gate 120, an insulator layer 130, an amorphous layer 140, an N-doped amorphous silicon layer 150, a source 160 and a drain 170. A material of the gate 120 is alloy utilized for turning on or off the electrical channel in the amorphous layer 140. The gate 120 is coated with the insulator layer 130 which is made of silicon nitride to prevent the gate 120 and the amorphous layer 140 from electrically connected. The amorphous layer 140 is disposed on the insulator layer 130 to be served as the channel for transmitting electrons. A portion of the amorphous layer 140 is covered with the N-doped amorphous silicon layer 150 to be served as an ohmic contact layer, so as to lower the impedance between the source 160 and the amorphous layer 140 and between the drain 170 and the amorphous layer 140. The materials of the source 160 and the drain 170 are metal and they are disposed on the N-doped amorphous silicon layer 150.
An electrical channel will be formed on the bottom of the amorphous layer 140 while a voltage is applied to the gate 120 of the thin film transistor 100. The electrons can be flowed to the drain 170 through the electrical channel while another voltage is also provided to the drain 170. The electrical channel formed on the bottom of the amorphous layer 140 will be disappeared while no voltage is provided to the gate 120, so the source 160 and the drain 170 have become open circuit. However, because the conventional thin film transistor 100 is not a flawless switch actually, the source 160 and the drain 170 is not an absolutely open circuit whether no voltage or a negative voltage is provided to the gate 120. In other words, little current will be still flowed through the N-doped amorphous silicon layer 150 and the surface of the amorphous layer 140 to be the leakage current between the source 160 and the drain 170 when the conventional thin film transistor 100 is turned off. For instance, if the voltage difference between the source 160 and the drain 170 is 10V and the voltage of gate is −6V, the leakage current between the source 160 and the drain 170 is about 10−11 and 10−12 amp.